What We Still Don't Know About Earthquakes

Nov. 14

Page 2 of 2

Engineers say high-rise buildings can be designed to withstand catastrophic quakes, but that concept has never been tested because no modern urban center has been hit with a major quake of, say, magnitude 8.5 since the beginning of the high-rise age. Cities like Tokyo, Los Angeles, San Francisco and Seattle are still waiting to see if the engineers are really right.

The Unknowns: ‘What’ and ‘When?’

We know what causes earthquakes. Quakes are caused by the sudden release of strain that builds up in the giant tectonic plates as they grind against each other while moving around the surface of the earth.

But we don't know specifically what triggers a quake. We do know it isn't the alignment of the planets, or radiation from space, or your grandmother's gout. The trigger probably varies with local conditions.

And nobody knows precisely when the next quake will occur. Instead of predicting quakes, scientists have settled for long-range forecasts.

So no reputable scientist is going to tell you that California's notorious San Andreas Fault is going to rip up that pricey landscape at 2 p.m. on Friday the 13th. The best they can do is say that some part of it is likely to break loose sometime in the next decade or so.

Faulty Timing

But there is some pretty convincing evidence that even those long-range forecasts are built on shaky ground. Most governmental agencies around the Pacific Rim base their engineering requirements on the idea that faults tend to rupture at fairly definable intervals. It's called the "time-predictable recurrence model," but it may well be dead wrong.

Geophysicists at Stanford University have taken a hard look at that concept and concluded that nature really isn't all that tidy when it comes to scheduling earthquakes. Jessica Murray and Paul Segall examined a famous section of the San Andreas Fault that runs through the farming village of Parkfield in central California.

Parkfield is the most instrumented fault zone this side of Tokyo because some decades ago scientists determined that it has ruptured on average once every 22 years since 1857. Since the last quake hit there in 1966, scientists began packing all sorts of gizmos into Parkfield in the mid-1980s. They reckoned that a quake of magnitude 6 should hit there by around 1987.

Most of those instruments are still there, and new experiments are being set up, but guess what? No earthquake. The shaker is way past due, but so far the score is San Andreas 1; scientists 0.

The Known: Unanswered Questions Remain

So where does that leave us? With a lot of questions.

We know we can build strong buildings. But are they strong enough?

We know what causes earthquakes. But are we ever going to be able to say when?

But there is one thing you can bank on. Sometime in the near future, someone in Congress or the federal Administration will try to whittle away at the already feeble budget for earthquake research.

That ought to shake you up.

Lee Dye’s column appears weekly on ABCNEWS.com. A former science writer for the Los Angeles Times, he now lives in Juneau, Alaska.